And the moral of the story is ...

... the "E" light on the fuel gauge of my new car does not mean "you have enough petrol left to drive to work a couple of times and fill up next time you remember to drive past a gas station".

What it actually means is "you have enough petrol to drive to a gas station RIGHT NOW or else you are going to end up sitting in the car park at work two days after the light first came on ringing your husband and asking him to come and rescue you".

Or something like that.